title: Magnetic field dependence of the diffusion of single dextran molecules within a hydrogel containing magnetite nanoparticles.
abstract: We consider the effect of applied magnetic fields on the diffusion of single dextran molecules labeled with fluorescein isothiocyanate within a ferrogel [a composite of magnetite nanoparticles in a poly(methacrylic acid) hydrogel] using fluorescence correlation spectroscopy. We show that the mesh size of the ferrogel is controlled by the applied magnetic field, B, and scales as exp(-(4)√ξ(3)B(2)/2μ(0)k(B)T), where ξ is a correlation length, μ(0) the magnetic constant, k(B) the Boltzmann constant, and T is the absolute temperature. The diffusion coefficient of the dextran can be modeled with a simple Stokes-Einstein law, containing the same scaling behavior with magnetic field as the swelling of the hydrogel. Furthermore, the magnetic field-dependent release of dextran from the hydrogel is also controlled by the same relationship. The samples were characterized by small angle x-ray scattering (SAXS) and magnetometry experiments. Magnetic hysteresis loops from these ferrogels and zero field cooled∕field cooled measurements reveal single domain ferromagnetic behavior at room temperature with a similar coercivity for both as-prepared and fully swollen ferrogels, and for increasing magnetic nanoparticle concentration. SAXS experiments, such as the hysteresis loops, show that magnetite does not aggregate in these gels.
authors.affiliation: Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, United Kingdom.
authors.forename: Ateyyah M
authors.initials: AM
authors.lastname: Al-Baradi
authors.forename: Oleksandr O
authors.initials: OO
authors.lastname: Mykhaylyk
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Blythe
authors.forename: Mark
authors.initials: M
authors.lastname: Geoghegan
mesh_terms: D003911:Dextrans / Q000737:chemistry*; D004058:Diffusion; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry*; D008280:Magnetics; D011109:Polymethacrylic Acids / Q000737:chemistry*; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D003911:Dextrans; D011109:Polymethacrylic Acids; C030613:polymethacrylic acid; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate